Polysiloxane polyols are well known in the art. Japanese Patent Publication 48-19941 describes polysiloxane polyols which are obtained by the dehydrogenation reaction between a polysiloxane hydride and an aliphatic polyhydric alcohol or polyoxyalkylene alcohol to introduce the alcoholic hydroxy groups onto the polysiloxane backbone. In practice, however, it is difficult to obtain an industrially significant yield of such polysiloxane polyols because such a dehydrogenation reaction readily gels. Another problem encountered with this dehydrogenation reaction is the difficulty in obtaining a solvent capable of dissolving both reactants. Strongly hydrophilic alcohols such as polyglycerols are highly soluble in alcohols and water, but insoluble in hydrocarbon solvents. Polysiloxanes, however, are generally only soluble in hydrocarbon solvents such as toluene or n-hexane.
U.S. Pat. No. 4,431,789 to Okazaki et al. discloses a polysiloxane polyol which is obtained by the dehydrosilylation reaction between a polysiloxane containing silicon hydride and a polyglycerol compound having an aliphatically unsaturated linkage in the molecule. Examples of such polyglycerol compounds are those obtained by the reaction of allyl alcohol and glycidol or by the reaction of diglycerin and allyl glycidyl ether. This reaction, a so-called hydrosilylation reaction, is the addition reaction between an organosilicon compound having a hydrogen atom directly bonded to the silicon atom, i.e., a polysiloxane hydride, and an organic compound having aliphatic unsaturation in the molecule carried out in the presence of a catalytic amount of a Group VIII noble metal. The hydrosilylation reaction can proceed readily in the presence of an alcoholic solvent which can dissolve both reactants. The resulting polysiloxane polyols are useful as non-ionic surface active agents. As each polyglycerol group provides only one terminal primary hydroxyl, the capacity of the polysiloxane polyol to crosslink with curing agents such as isocyanates, anhydrides and aminoplasts is somewhat hindered.
U.S. Pat. No. 5,260,469 discloses butoxylated polysiloxane polyols which are disclosed as being useful in cosmetics.
As aforementioned, the references teach the introduction of pendant alcoholic hydroxyl groups into a polysiloxane backbone via hydrosilylation of a polysiloxane containing silicon hydride with a polyhydric alcohol or polyoxyalkylene alcohol to form a polysiloxane polyol. Each pendant group, however, provides only one terminal primary hydroxyl group and at least one secondary hydroxyl group. There is no indication in the references, however, to hydrosilylate a polysiloxane containing silicon hydride with an alkenyl polyoxyalkylene alcohol which provides more than one terminal primary hydroxyl group.
Primary hydroxyl groups react more readily than do secondary hydroxyl groups with curing agents such as polyisocyanates, anhydride functional materials, aminoplasts and blocked isocyanates. Polysiloxane polyols containing multiple terminal primary hydroxyl groups would, therefore, provide improved cure rate and increased crosslink density. Accordingly, it is desirable to provide a polysiloxane polyol wherein at least a portion of the groups pendant therefrom have more than one terminal primary hydroxyl group per pendant group.